Over a number of years, methods have been developed for measuring carbon dioxide transport and associated mechanisms in animal tissues. These methods are now being applied in analyzing carbon dioxide excretion in mammalian lungs and muscles. In lungs we propose to measure CO2 permeability of tissue having intact membrane and cellular structure, and CO2 diffusing capacity of isolated lobe preparations. Because bicarbonate ions and their interconversion with CO2 gas are a consideration in CO2 transport, we will determine the extent to which lung carbonic anhydrase catalyzes this reaction in plasma of blood flowing through pulmonary capillaries. The role of carbonic anhydrase in CO2 transport between blood and alveolar gas will also be determined. Assays of lung tissues will be performed to determine the amount and activity of pulmonary carbonic anhydrase. The diffusion rate of CO2 in striated, cardiac and smooth muscle will be measured, and the extent to which it is controlled by carbonic anhydrase determined. Carbonic anhydrase activity of these muscle tissues will also be assayed. An attempt will be made to reconcile the observed CO2 diffusion transport, and particularly its change with carbonic anhydrase inhibition, with the measured carbonic anhydrase activity of lung and muscle tissue.